Electrochemical Corrosion Tests in Low-Conductivity Ethanol-Gasoline Blends: Application of Supporting Electrolyte for Contaminated E5 and E10 Fuels.

Ethanol-based E5 and E10 fuels have extensively been used as automotive fuels in gasoline engines. However, especially when contaminated, these fuels can exhibit corrosion effects on some engine construction parts such as mild steel. Thus, the study of mild steel corrosion resistance has become of the utmost importance. Electrochemical methods such as electrochemical impedance spectroscopy (EIS) and polarization characteristics measurements (Tafel scan-TS) were proven to be very valuable in studying the mild steel corrosion behavior in ethanol-gasoline blends (EGBs). However, the use of these methods was, so far, very limited for low-ethanol-content EGBs such as E5 and E10 due to their low conductivity. In this study, we present modified EIS and TS corrosion measurements based on the use of tetrabutylammonium tetrafluoroborate (TBATFB) at 500 mg/L as a supporting electrolyte. This modification led to an increase in the contaminated E5 and E10 fuels' conductivity, which allowed us to successfully perform the electrochemical corrosion tests. The corrosion current densities were determined to be 1.5 × 10-3 and 1.5 × 10-2 µA/cm2 for the tested E5 and E10 fuels, respectively. These modified methods present a significant extension of an electrochemical testing apparatus for steel corrosion studies in EGBs. They can allow one to obtain instantaneous information about the occurring corrosion process and, thus, estimate the materials' lifetime in corrosive environments and potentially help to prevent corrosion.

Electrometric bromine number as a suitable method for the quantitative determination of phenols and olefins in hydrotreated pyrolysis bio-oils.

Bio-oils after hydrotreatment can still contain significant amount of phenols and cyclic olefins as the products of an incomplete deoxygenation. The removal of these compounds would be necessary to produce suitable components for automotive fuels. However, no routine method currently exists for the reliable determination of these groups in hydrotreated bio-oils (HBOs). In this paper, we analyzed 140 different pure oxygenates as model compounds using the bromine number method (ASTM D1159) observing that most compounds present in HBOs react with one equivalent of bromine. The determination of phenols using bromine number method in crude bio-oil is complicated especially by the presence of guaiacols and syringols that react with more than one equivalent of bromine and, thus, the obtained result is significantly overestimated. Further we optimized the chromatographic separation of hydrocarbons from HBOs for the selective determination of olefins content. As no other reactive compounds under the conditions of the method, besides phenols and olefins, were observed in HBOs, the difference between HBO bromine number (before hydrocarbons separation) and olefins content correspond to the total amount of phenols. The method was finally applied to 11 HBOs with different content of oxygen, providing a good correlation between phenols and oxygen content.

Cyclic Potentiometric Polarization and Resistance of Mild Steel in an Environment of Alcohols and Their Blends with Gasoline.

Nowadays, there is an effort to increase the more widespread use of biofuels that are a renewable energy source in transportation and an alternative to conventional, petroleum-based fuels. These biofuels include alcohols such as biomethanol, bioethanol, and biobutanol that have a high octane number, but generally different physical and chemical properties than petroleum fuels. The different properties of alcohols may cause low material compatibility with carbon steel. Here, we used cyclic potentiodynamic polarization (CPP) to study the behavior of carbon steel in an environment of alcohols and alcohol-gasoline blends (AGBs). Using CPP, we proved that the corrosion of mild steel can be significantly influenced by alcohol properties, such as the chain length, pK a, and solubility of oxygen and water. In the environment of pure alcohols (not blended by gasoline), a very good passivation ability of steel was proven, especially for n-butanol. In AGBs, steel corrosion can also be influenced by the gasoline amount. When these pure alcohols or their gasoline blends are contaminated by water-containing chlorides and organic acids, the corrosion rate of carbon steel can increase by up to 4 orders of magnitude. In an anhydrous environment of alcohols, the CPP can give results with a very good informative value.

Efficiency of Steel Corrosion Inhibitors in an Environment of Ethanol-Gasoline Blends.

Ethanol produced from renewable sources (i.e., bioethanol) is a first-generation biofuel that is currently being added as a biocomponent into gasolines. Mixtures of ethanol and gasoline are designated as ethanol-gasoline blends (EGBs). Ethanol has high polarity and moisture affinity, which considerably influence the properties of the resulting EGBs including their aggressiveness to many metallic and nonmetallic materials. The corrosion aggressiveness of EGBs can be minimized by suitable corrosion inhibitors. In this study, we tested three different corrosion inhibitors on mild steel in the environment of aggressive E10, E25, E60, and E85 fuels. The inhibitors tested were diethylene triamine (DETA) and two mixed inhibitors containing propargyl alcohol, dibenzyl sulfoxide, and octadecyl amine. To study the efficiency of the corrosion inhibitors, we used static and dynamic corrosion tests and electrochemical measurements including impedance spectroscopy and potentiodynamic polarization. The highest corrosion aggressiveness on mild steel was observed for the E60 fuel. The highest inhibitory efficiency was, for all the fuels tested, observed for the DETA inhibitor. For the DETA concentration of 100 mg·L-1, the inhibitory efficiency in the E60 fuel was determined to be around 98%.

Metal Corrosion and the Efficiency of Corrosion Inhibitors in Less Conductive Media.

Material corrosion can be a limiting factor for different materials in many applications. Thus, it is necessary to better understand corrosion processes, prevent them and minimize the damages associated with them. One of the most important characteristics of corrosion processes is the corrosion rate. The measurement of corrosion rates is often very difficult or even impossible especially in less conductive, non-aqueous environments such as biofuels. Here, we present five different methods for the determination of corrosion rates and the efficiency of anti-corrosion protection in biofuels: (i) a static test, (ii) a dynamic test, (iii) a static test with a reflux cooler and electrochemical measurements (iv) in a two-electrode arrangement and (v) in a three-electrode arrangement. The static test is advantageous due to its low demands on material and instrumental equipment. The dynamic test allows for the testing of corrosion rates of metallic materials at more severe conditions. The static test with a reflux cooler allows for the testing in environments with higher viscosity (e.g., engine oils) at higher temperatures in the presence of oxidation or an inert atmosphere. The electrochemical measurements provide a more comprehensive view on corrosion processes. The presented cell geometries and arrangements (the two-electrode and three-electrode systems) make it possible to perform measurements in biofuel environments without base electrolytes that could have a negative impact on the results and load them with measurement errors. The presented methods make it possible to study the corrosion aggressiveness of an environment, the corrosion resistance of metallic materials, and the efficiency of corrosion inhibitors with representative and reproducible results. The results obtained using these methods can help to understand corrosion processes in more detail to minimize the damages caused by corrosion.